To package a device in plastic, a typical die having an integrated circuit in a top face is bonded onto a paddle so that the bottom face of the die is bonded to the paddle. The die is then coupled to a leadframe with wirebonds. The die, paddle, and leadframe are encapsulated in plastic by flowing plastic over them at high temperature and pressure. This typical encapsulating process cannot be used with some dies, such as micromachined devices that have movable components, because the flowing plastic would affect the movement of the movable components.
Instead of packaging in plastic, some devices are packaged in hermetic containers to keep moisture away from the die. Several different types of packages are used, including a ceramic dual in-line package (cerdip), a ceramic side braze package, and a generally cylindrical metal package.
In such packages, the die is typically bonded to the inside of the package with a die attach, and then the package is sealed. A typical die attach in a cerdip process uses a silver paste. Such a paste can provide stress to a die, thus potentially degrading long-term performance.